"Getting away with it" is exactly what you'd be doing (and I do)... it's really not ideal to use anything BUT a professional field/production monitor - but not all of us have that kind of money.

On my last short I just plugged the AV lead from my camera into a very cheap 14" TV set up as the field monitor - but I was only using it to frame shots, so it was perfect. During the shoot myself and the AD watched the TV for the performance, shadows, reflections etc...

Future shoots I'll just be using a 7" LCD instead (as a lightweight set-up is important for me), use what you can afford - or hire a field monitor for the shoot.

It's important to note, though, that a TV won't show the whole picture, just the TV safe areas. When you're shooting something that will be shown in a cinema (eg. festivals) or on LCD/plasma screens where TV safe areas aren't an issue - then you MUST allow for this in framing... you don't want runners or mic booms on the edges of your shot!